A method and means for detecting faults or defects in moving machine parts are disclosed in British Pat. No. 1,603,190. In this known means, the transducer, which is a mechanically tuned accelerometer, is tuned so that its resonance frequency lies in the range of 30-40 kHz, so that the greatest sensitivity of this transducer likewise lies in this frequency range. This is coincident with the resonant frequency range of the expected vibrations. In this known method and means, use is made of the resonance peak of the transducer to improve the selectivity and amplification. In practice, however, problems arise when bearings of average size, for example, are tested for defects by detecting the mechanical vibrations, because their resonant frequencies and the second and third harmonics thereof all lie in the same frequency range of 30-40 kHz. Thus, the mechanical amplification of given frequency bands in a machine part on which the measurement is being made may be greater than the mechanical amplification of the transducer. The means described in British Pat. No. 1,603,190 is, accordingly, sensitive to disturbance signals making reliable detection of faults and defects impossible. The vibrations that are generated by faults or defects cause standing waves to be produced on the surface of the machine on which the transducer is mounted. The wavelength for frequencies of 40 kHz, for example, is 150 mm, making it difficult to determine a suitable position for the transducer, since there is the chance that the transducer will be placed at a node and nothing would be measured.
The object of this invention is to provide a method and means for detecting faults or defects in moving machine parts wherein these disadvantages are avoided in a simple but nevertheless effective way.